In the related art, a battery pack in which a block is constructed by connecting one or a plurality of batteries in series and a plurality of the blocks are connected in series is equipped in a hybrid automobile and an electric automobile, and a device for measuring voltage or current of each block of the battery pack and detecting abnormality has been developed. A basic method of detection of the abnormality is that a voltage and a current are measured for each block and an internal resistance (IR) is calculated through the method of least squares. The abnormality is detected based on an increase or a deviation of IR.
FIG. 12 shows a result of a plot of current against voltage for a block obtained through measurement, with the horizontal axis representing the current and the vertical axis representing the voltage (block voltage). In FIG. 12, the X mark represents each measurement point. A straight line 50 is a straight line obtained by the method of least squares based on the plurality of measurement points, and the slope of the straight line represents the IR. For each block of the battery pack, a straight line is calculated, and when the straight lines are in an allowable range, the battery pack is determined to be normal. On the other hand, as shown in FIG. 13, when a straight line 60 of a certain block has a large deviation with respect to the straight lines 50 of the other blocks when the straight lines are calculated through the method of least squares for each block, the abnormality of the battery pack is detected by determining that IR has increased due to elapse of the lifespan, compromising of airtightness, etc.
JP 2001-196102 A discloses a technique of detecting abnormal increase in temperature of the battery in which the IR of each block is calculated based on the block voltage and the current and the IR is compared with a predetermined threshold value. FIG. 14 shows a structure of the battery pack control device disclosed in this reference. The battery pack control device is equipped in a hybrid automobile. The battery pack control device controls input and output of a battery pack 10. The battery pack 10 comprises a plurality of blocks 10A which are connected in series. Each of the plurality of blocks 10A comprises a plurality of single batteries 10B which are connected in series. The battery pack control device comprises a battery power input and output section 1 which controls an input and an output of power of the battery pack 10, a block voltage detecting section 2 which detects a block voltage of each of the plurality of blocks 10A, a battery current detecting section 3 which detects a battery current of the battery pack 10, an abnormal temperature increase detecting section 4 which detects abnormal temperature increase of the single battery 10B based on the block voltage and the battery current, a vehicle control section 5 which controls the battery power input and output section 1 based on a detection result of abnormal temperature increase by the abnormal temperature increase detecting section 4, and a battery temperature detecting section 6 which detects a battery temperature of the battery pack 10. The abnormal temperature increase detecting section 4 comprises an internal resistance calculating section 4A which calculates an internal resistance of each of the plurality of blocks 10A based on the block voltage and the battery current, a threshold value setting section 4B which sets a threshold value based on the battery temperature of the battery pack 10, a variance calculating section 4C which calculates an average value and a variance σ2 of the block voltage of each of the plurality of blocks 10A, a variance abnormal temperature increase detecting section 4D which detects an abnormal temperature increase of the single battery 10B based on the block voltage, average value, and variance σ2 of each of the plurality of blocks 10A, and a remaining capacitance abnormal temperature increase detecting section 4E which detects abnormal temperature increase of the single battery 10B based on a remaining capacitance of each of the plurality of blocks 10A. The battery power input and output section 1 comprises an inverter 1A of a hybrid automobile and a motor generator 1B. The motor generator 1B drives an engine 12 through a transmission 11. An engine control section 13 controls the engine 12 based on an output of the vehicle control section 5. The vehicle control section 5 is connected to an acceleration pedal 7, a braking pedal 8, a shift lever 9, and a battery remaining capacitance detecting section 14. The vehicle control section 5 controls the battery power input and output section 1 based on a detection result of the abnormal temperature increase by the abnormal temperature increase detecting section 4.
JP 2005-195604 A discloses a technique in which a voltage of each of a plurality of batteries of a battery pack is measured at a predetermined time and the current flowing through the battery pack is measured at the same time, a difference between the maximum value and the minimum value of each voltage obtained through the measurement is calculated, and the abnormality of the battery pack is detected based on values of the pair of the current and the difference.
However, in the structure of measuring the block voltage and the current for each block, an A/D conversion is required for the block voltage, which may result in an increase in the cost. In addition, because the IR is calculated through the method of least squares based on the block voltage and the current, there is a problem in that the processing time is increase and the load of the processing program is increased due to the increase in the amount of calculation. In addition, when the speed of the calculation is increased in such a state, heat generation may result, which may prevent size reduction of the detection device.